The figure of Yahya—an English-speaking convert within ISIS with powerful connections and the cojones to challenge Baghdadi to a death match—intrigued me. But Cerantonio didn’t elaborate on his identity and referred to him only by an alias, in the traditional Arabic style, with his first name and the name of his firstborn: Yahya, father of Hassan. He said Yahya was a fellow Dhahiri—a member of an obscure, ultra-literalist legal school that had enjoyed a sort of revival within the Islamic State. He didn’t, or wouldn’t, say more. I wrote down the name and committed to investigating Yahya later. ... Soon enough, I began collecting clues to his identity.